U. S. DEPARTMENT OF AGRICULTURE. 



q k. Gilbert. 



CONDITIONS IN SOILS OF THE ARID REGION. 



HY 



MILTON WHITNEY, 

Chief of the Division of Agricultural Soils. 



[Reprinted froen the Yearbook of the U. S. Department of Agriculture for 1894.] 




WASHINGTON: 

GOVERNMENT PRINTING OFFICE. 
1-895. 



U. S. DEPARTMENT OF AGRICULTURE. 



CONDITIONS IN SOILS OF THE ARID REGION. 



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BY 



MILTON WHITNEY, 

Chief of the Division of Agricultural Soils. 



[Reprinted from the Yearbook of the U. S. Department of Agrisulture for 1894.] 




WASHINGTON: 

GOVERNMENT PRINTING OFFICE. 
1895. 



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CONTENTS 



Page. 

Arid and humid regions compared 157 

Depth of soil moisture 159 

Hot winds 162 

Advantages of understanding soil conditions , 163 

Subsoiling 163 



ILLUSTRATION. 



Page. 
Fig. 11. Average yield of corn in bushels per acre in Kansas, sixteen years. .. 158 



(A portion of the article entitled '■ Soils in their Relation to Crop Production, " in the Yearbook of the 
U. S. Department of Agriculture, 1894. 



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CONDITIONS IN SOILS OF THE ARID REGION. 

By Milton Whitney, 
Chief of the Division of Agricultural Soils, U. S. Department of Agriculture. 

The so-called arid portion of Kansas and Nebraska is, broadly speak- 
ing, that portion of the States lying west of the one hundredth merid- 
ian; between the one hundredth meridian and the ninety-seventh the 
climate is called semiarid; and east of the ninety-seventh is the humid 
portion of the States. The mean annual rainfall of the western or 

155 



156 YEARBOOK OF THE U. S. DEPARTMENT OF AGRICULTURE. 

arid portion is from 15 to 20 inches ; of the central or semiarid portion, 
from 20 to 30 inches; and of the eastern or humid portion, 30 inches 
and over. There are of coarse no sharp lines separating these divis- 
sions, nor do the boundaries approach a north and south line, for the 
belts of greater or less precipitation have very sinuous courses. 

It is generally conceded that 20 inches of well- distributed rainfall in 
Kansas will make an abundant crop of wheat or corn. That there 
must be some rather anomalous condition here is shown by the fact that 
in much of the humid portion of the eastern United States there has 
never been so little as 20 inches of annual rainfall within the period of 
reliable records, and in years of most disastrous drought the rainfall 
has been greater than this. The fact that a crop can be made in Kansas 
and Nebraska with such a small annual rainfall is particularly striking 
when it is remembered that, owing to the drier conditions of the atmos- 
phere, evaporation is very much greater there than in the East. 

There are localities in the West where the total annual rainfall does 
not exceed 6 or 8 inches. It does not seem possible that with this 
rainfall under ordinary circumstances crops could be produced by any 
system of agriculture, unless water were artificially supplied. How- 
ever, it seems possible, outside of these exceptional cases, that with 
improved methods of cultivation the conditions actually existing can 
be so utilized as to secure reliable and satisfactory crops. 

Statistics show that in the humid portion of the United States, hav- 
ing a mean annual rainfall of about 40 inches, 50 per cent flows off into 
the streams and is of no direct benefit to agriculture. This excess of 
rainfall reaches the streams partly by flowing over the surface of the 
ground and partly by slow percolation through the soil. Fifty per cent 
of the rainfall, or 20 inches per annum, evaporates directly from the 
surface of the soil or is transpired by plants. 

Practically, therefore, there are about 20 inches of rainfall at the 
disposal of agricultural plants, and the highest art of cultivation con- 
sists in conserving this moisture, reducing that lost by evaporation from 
the surface soil to a minimum, and maintaining a sufficient amount at 
all times at the disposal of crops. 

There is one factor which has a very important bearing upon the con- 
ditions in the humid as compared with those in the arid regions. In 
the humid region of the Eastern States the soil is continuously moist 
from the surface down to a depth at which it is completely saturated 
and from which water is constantly flowing out into wells, streams, and 
rivers. The water descends through the soil both by virtue of its own 
weight and by capillary force. According to capillary laws the water 
is pulled downward when the subsoil contains less water than the soil. 
Gravity and capillary force are both more effective in moving water 
through a moist subsoil than a dry one; hence there is danger in the 
East of the water being pulled down below the reach of plants in time 
of drought, while in the West, where the subsoil at the depth of a few- 
feet is continuously dry, this could not happen. 



EELATION OF SOILS TO CROP PRODUCTION. 157 

Plants may be likened to a pump, which must have a steady and suf- 
ficient stream flowing into the well lest the surface of the water shall 
fall below the valve and the pump become inactive while there still 
remains a considerable amount of water in the well. There must be an 
adequate supply of water in the soil for the plants to draw upon, and 
this supply must be within their reach. To illustrate : A plant may wilt 
in a soil of close texture containing 10 or 12 per cent of moisture, 
because with so little water present in the soil the movement of water 
to the roots of the plant would be comparatively slow, and the volume 
supplied per minute or per day would be insufficient; the plant would 
quickly exhaust the supply in the immediate neighborhood of its roots, 
and the amount necessary for its continued growth could not be pulled 
up from the surrounding soil rapidly enough to make good the loss. In 
a soil of different texture the same plant may not suffer until the sup- 
ply falls to 4 or 6 per cent. 

ARID AND HUMID REGIONS COMPARED. 

There must, therefore, be a certain minimum amount of moisture in 
all soils, just as there must be more water in a well than the pump will 
ever use. This minimum amount will depend upon the structure of the 
soil and the rate of movement of moisture and upon the requirements 
of the plant. An ordinary rainfall will have a far more beneficial 
effect upon the crop growing on a soil which contains this minimum 
amount than upon a crop growing on a soil containing less than the 
minimum. It must also be borne in mind, in comparing the soil con- 
ditions of the humid and arid regions, that the excess of moisture in 
the humid regions may often be of indirect value to agriculture by 
increasing the availability of the moisture which is to remain. 

In the arid portions of Kansas, Nebraska, and Colorado, with a mean 
rainfall of nearly or quite 20 inches per annum, statistics of the gauging 
of rivers and streams show that 10 per cent, or 2 inches, of this rain- 
fall flows off into streams and is of no direct benefit to agriculture. 
This gives, broadly speaking, 18 inches of rainfall available for agricul- 
ture in the arid regions as against 20 inches of available rainfall in the 
humid portion of the United States. Statistics show likewise that the 
greater portion of this rainfall in the arid region comes during the grow- 
ing season. From April to the last of August they have an average 
rainfall of between 3 and 4 inches a month. 

It appears at first sight a rather anomalous fact that there is nearly 
as much available rainfall in the arid as in the humid region; but there 
are several modifying circumstances that must be borne in mind. In 
the first place, the humidity of the atmosphere is very much less aud 
evaporation is very much greater in the climate of the arid region. 
Statistics show that the annual evaporation from a free-water surface 
in the arid region is about 60 or 80 inches. In the humid portion of 
the Uuited States the evaporation from a free- water surface is equal to 



158 YEARBOOK OF THE U. S. DEPARTMENT OF AGRICULTURE. 

about 30 inches per annum. Roughly speaking, therefore, the amount 
of evaporation is twice as great in the arid region under consideration 
as in the humid portion of the country. Relatively more of the rain- 
fall would therefore evaporate from the soil and relatively less would 
be available to plants. It would also seem that plants would transpire 
much more water and would require a more abundant water supply in 
the arid climate. It will be remembered, too, that there is practically 
no excess of water in the soils as in the soils of the humid region 
to make these 18 inches more available to plants. 





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Pig. 11. — Average yield, of corn in bushels per acre in Kansas, 16 years. 

The fact remains, however, that in years of normal rainfall well dis- 
tributed over the growing season, small though it is, a good crop is 
obtained throughout the semiarid region, and even on the so-called arid 
plains, where the land is properly cultivated. Statistics compiled by 
tbe Kansas board of agriculture show that in the sixteen years from 
1877 to 1892, inclusive, the yield of corn per acre in the State of Kansas 
exceeded 30 bushels in eight seasons and the yield fell below 20 bushels 
per acre in three seasons. This is shown graphically in the accompany- 
ing illustration (fig. 11). 



RELATION OF SOILS TO CROP PRODUCTION. 159 

The average yield of wheat during this same period exceeded 15 
bushels per acre during seven seasons and was under 11 bushels per 
acre five seasons. In the arid portion of the State a fairly good season 
occurs about two years in five, the remaining three out of the five 
seasons being too dry for a good crop. The fact that they can make a 
crop at all with an annual rainfall of 20 inches under the conditions 
which have already been considered is surprising, and indicates that 
there must be conditions which are not strictly comparable with those 
in the humid region, and that there are advantages to counteract the 
apparently unfavorable conditions. 

DEPTH OF SOIL MOISTURE. 

A considerable portion of the 2 inches of annual rainfall of the arid 
region which finds its way into streams and rivers must flow off over 
the surface and not even enter the soil. The extreme and rapid varia- 
tion in the volume of the rivers, and the frequent torrential showers, 
during which the ground is flooded with water, indicate that this con- 
dition does in fact prevail to a large extent. Some water is retained 
by local depressions until it sinks, and there are undoubtedly soils of 
loose, light texture into which a considerable amount descends and finds 
its way to the rivers and streams by slow percolation; but as a rule 
there seems to be no connection between the surface moisture and the 
underlying " water table." The natural prairie sod sheds water like a 
roof when it is delivered rapidly and in large volume, and it is only 
with a long continued, gentle rain that the soil and subsoil under the 
sod will absorb any considerable amount of moisture. 

During a recent examination of the conditions in the soils of the 
plains of western Kansas, Nebraska, and eastern Colorado, no trace of 
moisture was found in a number of borings from just below the surface 
to a depth of 3 feet under the natural prairie sod, except on the light 
soils of the sand hills near Garden City and in a few depressions, where 
water had evidently been caught. The season had been exceptionally 
dry, but an inch of rain had fallen about a week before the examina- 
tions were made. Where the sod had been broken and the land had 
been under cultivation during the season the subsoil was quite moist, 
and more moist the more thorough the cultivation had been. 

At Geneva, Kebr., the soil and subsoil immediately under the prairie 
sod was so dry that it was extremely difficult to take a sample with an 
auger, both because it was hard to bore into and because the material 
loosened by the auger was so dry and powdery that it ran off the auger 
like fine, dry dust or sand. In an oat field, which had been thoroughly 
prepared by subsoiliug two years before, the subsoil was quite moist, 
although the ground had not been actually cultivated for a year. In 
an adjacent field which had been subsoiled the previous year, and dur- 
ing the present year had been thoroughly cultivated in nursery stock, 
the subsoil down to a depth of 3 feet was so moist that it could be 



160 YEARBOOK OF THE U. S. DEPARTMENT OF AGRICULTURE. 

molded in the hand. These three localities were not over a few hun- 
dred feet apart and had been exposed to precisely the same rainfall, 
but had been subjected to these different methods of cultivation. 

It is a common inquiry in the arid region after a rain, how far the 
moisture has descended, or, generally, how far it is down to dry soil. 
The evidence of well-diggers is that after passing, through the upper 
few feet of earth the underlying material is dry until they approach 
the water-bearing layers of sand and gravel. The fact of the accumu- 
lation of alkalies shows that the subsoil is not continuously wet down 
to the "water table," as otherwise these would be leached out and car- 
ried off through the subsoil as they are formed. 

Water descends very slowly and to a very limited extent in a per- 
fectly dry soil, while it will spread out very rapidly in a soil which is 
already moist, but short of actual saturation. Water may fall for days 
upon a pile of dry manure and not wet the mass deeper than a few 
inches. Water may likewise fall upon a dry dust pile and not spread 
through the mass, but be contained near the surface, unless it continues 
to fall, in which case the whole mass of the dusty material may become 
saturated. Water does not readily spread through a previously dry 
soil, because the tension or contracting power of the surface of the 
water is greater than the attraction of the soil grains, which tends to 
cause its diffusion through the mass. One may see, therefore, a nearly 
saturated layer closely adjacent to a perfectly dry and dusty mass. On 
the other hand, if there is any appreciable amount of moisture in tbe 
soil the tension of the water surface will cause it to contract and pull 
water from above into the subsoil. 

It would follow, therefore, that the moisture would not descend into 
the dry subsoil of the upland prairie until the successive depths had 
become so far saturated that they could no longer hold the water back, 
and it would pass downward very gradually into the lower depths sat- 
urating, or nearly saturating, each successive depth as it progressed. 
Unless the rainfall was so great and so continuous as to saturate the 
soil to a considerable depth, the water would not pass down to a great 
extent in the dry material. The whole supply of moisture absorbed by 
the soil would remain within a short distance of the surface, and when 
evaporation was started again from the surface or the moisture was 
used up by plants the water would be pulled up again from the depths 
to which it had progressed rather than proceed on its downward course. 
There is less force to pull it down into the dry subsoil than its own con- 
tracting power, which pulls it up through the moist soil to the plant or 
to the surface of the ground. 

It appears probable, therefore, that in the more retentive soils of 
the arid regions the whole of the 20 inches of rainfall, or as much of 
this as is absorbed by the soil, will be held within a few feet of the 
surface, within easy reach of the roots of plants. The problem should 
be how to conserve the moisture, diminish the evaporation from the 



RELATION OF SOILS TO CROP PRODUCTION. 161 

soil, and maintain as much as possible of the supply for the use of 
crops. 

Two things suggest themselves at once: The preparation of the soil 
must be sufficiently thorough and deep to insure the absorption of the 
whole amount of the rainfall, and preparation should be so thorough 
and deep that this water will be carried to a sufficient depth to dimin- 
ish the chances of surface evaporation and prevent the saturation of 
the upper soil, which would be prejudicial to plant growth. The water 
must be absorbed as deeply as possible, so as to check surface evapo- 
ration, and at the same time be maintained sufficiently near the surface 
to be available to plants as needed. Where water is of so much value 
and of such vital importance, not a drop of rainfall should be allowed 
to waste by flowing off over the surface. It should all be absorbed by 
the soil. The rains are often so torrential in character that the soil 
must be in a condition to absorb the water very rapidly to prevent 
any loss. 

The conditions actually existing in these soils should be made the 
subject of careful and thorough investigation. The amount of mois- 
ture actually maintained by the soils should be ascertained by daily 
determinations, to give a basis for working out improved methods of 
cultivation or planting for the conservation of moisture. The rainfall 
should be followed and its whole history worked out from the time it 
enters the soil. In the first place, how deep does the rainfall penetrate 
into the different soils of the plains? This could be ascertained at 
different depths at intervals of a week or ten days throughout the sea- 
son by moisture determinations. Is any of the rainfall drawn so low 
as to be unavailable to plants and lost by percolation into the "water 
table"? How much of the rainfall evaporates from the different types 
of soils, how rapid is this evaporation, and how even are the condi- 
tions which the principal soils maintain? What part of the moisture 
evaporates from the soil and what part is transpired by the growing 
crop? How much water does a plant transpire in the arid regions for 
every pound of dry matter produced as compared with the same class 
of crops in the humid regions? These are all fundamental questions, 
which will have to be understood in order to secure any intelligent 
improvement of the methods of cultivation and cropping. 

More than half of the annual precipitation in Kansas occurs in the 
four crop-growing months of April, May, June, and July. During May 
and June especially the frequent showers induce a very rank and lux- 
uriant growth, and there is nearly always up to the middle or end of 
June the prospect of a large corn crop. It is not uncommon, however, 
for a dry spell in July to reduce the promised yield by 100,000,000 or 
150,000,000 bushels. These dry spells last from two to four weeks, 
frequently resulting in great damage to the corn crop. 

Wheat is usually harvested before this midsummer drought comes 
on, and there is less variation in the yield of wheat in the State than in 



162 YEARBOOK OF THE U. S. DEPARTMENT OF AGRICULTURE. 

the corn crop. Such crops also as turnips, millet, and sorghum do very- 
well from the August rains. The drought comes frequently at the most 
critical time of all in the development of the corn plant— just as it is 
tasseling out. It should be possible to breed new varieties, maturing 
earlier or later, so as to secure a crop at a different stage of develop- 
ment during this usual summer drought. 

HOT WINDS. 

The very time when the crop is suffering from drought is the time of 
all others when hot winds are liable to occur. These winds blow at the 
rate of 20 to 30 miles per hour, the temperature of the air frequently 
ranging from 100° to 106°, with only 20 to 30 per cent of relative 
humidity. This vast body of dry, hot air passing over the crop induces 
such rapid evaporation that the roots can not possibly supply sufficient 
moisture, and the plants are completely desiccated, or dried out. The 
cells dry up to such an extent that they die, and the whole leaf struc- 
ture collapses and hangs limp and lifeless. The effect of hot winds 
upon the crop is markedly different from the effect of drought alone. 
In an ordinary drought the fodder dries and is cured much as if it had 
been cut and exposed to the sun and air, the plants, however, remain- 
ing erect. The effect of hot winds is much more quickly fatal to the 
crop; two or three days is often sufficient to destroy the most promis- 
ing field of corn. The evaporation from the plants under these condi- 
tions must be enormous. It is so excessive, indeed, that even with 
the soil quite moist the powers of the plant may be taxed beyond 
endurance. 

There are several possible ways to prevent or greatly lessen the injury 
from hot winds. Wind-breaks diminish the injurious effects of hot winds, 
for when the air is quiet the evaporation from the leaves increases the 
humidity of the air immediately around them, and this diminishes the 
evaporation from the leaf. If this air is removed, however, and quan- 
tities of dry air are rapidly presented to the plant the excessive evapo- 
ration is continued. Anything, therefore, which will retard the rate of 
movement of the wind will tend to diminish evaporation from the plants 
within the area of its influence. The more moist the soil can be kept 
through methods of cultivation the less damage there will be to vege- 
tation, for the roots will have a larger supply of moisture to draw from. 
The hot winds rarely do much damage over irrigated fields when the 
water supply can be properly controlled. The most disastrous effect 
of hot winds, however, frequently follow a rainfall occurring after a 
long period of drought. During the rain transpiration from the plant 
is checked and the cells become excessively turgid and possibly weak- 
ened through distention aud possibly by the presence of organic acids. 
When the hot winds immediately follow this abnormal condition of the 
plant, the evaporation is rapidly increased, the cells lose their water and 
collapse and die, as possibly they would not have done if the conditions 
preceding the hot winds had been more normal. 



ADVANTAGE OF SOILS TO CROP PRODUCTION. 163 

BENEFIT OF UNDERSTANDING SOIL CONDITIONS. 

It may be asked what advantage it would be to understand soil con- 
ditions and what control of them is possible. As regards the first 
question, this knowledge will make it possible intelligently to classify 
the soils according to the conditions which they maintain and predict 
what classes of crops they will prove adapted to grow. It would sug- 
gest also the way in which the soil conditions should be changed to 
make them correspond still more closely to the requirements of the 
class of crops to which they are most nearly adapted. As regards the 
second question, it is quite possible, through intelligent methods of 
cultivation, of cropping, and of fertilization, to change the conditions 
maintained by soils by changing their physical texture. It is likewise 
possible that we shall be able in time to control the amount of water 
taken up from a soil and transpired by plants. In a soil containing 
much water it should be possible to prevent the plant taking an 
excessive amount, thus checking the too luxuriant growth of vegeta- 
tion, or in a soil containing a small amount of moisture to induce the 
plant to take up more water than it otherwise would. This control 
will come through the effect of fertilizers and chemicals upon the roots 
which will stimulate or diminish the transpiration powers of the plant. 

SUBSOILING. 

Where the amount of rainfall is so small it is obviously important 
that the soil should absorb all of the rain which falls upon it. It is 
folly to allow water to flow off the farm, incidentally causing damage 
by washing, and then spend large sums to put in irrigation ditches to 
replace it by water which others have allowed to flow off their land. 
Wherever a drop of water flows off the field it is an indication that the 
soil is not in a proper physical condition. Where this occurs in a dry 
soil the main preparation of the land should be as deep as possible, so 
that the water may be carried down and thus diminish the rapidity 
of the evaporation and loss from the surface. If deep plowing will 
not accomplish this object, subsoiling will be found invaluable in open- 
ing up the close and compact subsoil. A subsoil plow should be as 
small and light in all its parts as is consistent with the great resistance 
it has to encounter. The point should be small and narrow, like the 
point of a pick, somewhat larger at the back than at the front. It is 
not necessary to have this large, for any implement which could be 
pulled through the subsoil would break and loosen it sufficiently to 
change its physical texture. There are some soils where subsoiling 
would not only be of no advantage, but in which it might be a positive 
injury to the land. A light, sandy soil having already an open and 
porous subsoil would not be benefited by having this subsoil made still 
more open. A farmer should judge whether subsoiling is advisable by 
the character and condition of the subsoil, and particularly witli a view 
to the question whether any part of the rainfall flows off the surface. 



164 YEARBOOK OF THE U. S. DEPARTMENT OF AGRICULTURE. 

The conditions in the arid regions are so different from those in the 
humid portion of the country that the methods adapted to the former 
are not necessarily well adapted to the latter. The act of subsoiling, 
the breaking up and stirring the soil to a depth of 12 or 15 inches, 
tends to dry it out; and unless a rain follows before a crop is put in 
the subsoiling may work positive injury to the first crop, although the 
beneficial effects would be felt in the succeeding crops. To secure 
benefit the first season the subsoiling must be done a considerable 
length of time before the crop is put in, in the hope of receiving heavy 
and long-continued rains. It is obvious that the nature of-the soil 
itself will largely determine the depth to which the cultivation should 
be extended, and the character of the season should determine at what 
time this cultivation should take place. It is very necessary in this 
deep cultivation of the soils of the arid regions that care be taken not 
to turn under a heavy sod or a quantity of organic matter, especially 
when the season or the soil is dry. In these dry soils a heavy sod or a 
lot of trash or stubble will not readily decay when turned under; 
indeed, it may remain undecayed for several years. In this condition 
it will break off capillary connection with the subsoil, so that if the 
crop is planted on the upturned sod it may actually perish for lack of 
moisture. It is a very common experience, nevertheless, with farmers 
on the plains that where the sod is broken very shallow, so shallow that 
the crop roots below it, the upturned sod acts as a very efficient mulch 
to prevent evaporation, and so increases the yield of crops. 

After a soil is once deeply prepared, the after cultivation of the crop 
should be as shallow as possible in order to maintain a mulch of loose, 
dry soil over the surface to check evaporation, yet to keep this mulch 
as thin as possible so as not to dry out more of the soil than is abso- 
lutely necessary. While cultivation should thus be very superficial, it 
should be frequent and continued well into the fruiting period of the 
crop. The old rule of giving one cultivation after each rain is not 
sufficient. 

Thorough preparation of the land, with subsoiling where this is nec- 
essary to break up a compact subsoil, followed by shallow but frequent 
cultivation of the surface, will undoubtedly make the crop much safer 
and surer in the arid and semiarid regions of the West. 



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